Move preference MACs to the protected preference stores.

chrome/browser/prefs/pref_hash_store.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PREFS_PREF_HASH_STORE_H_
 #define CHROME_BROWSER_PREFS_PREF_HASH_STORE_H_
 
 #include "base/memory/scoped_ptr.h"
 
+class HashStoreContents;
 class PrefHashStoreTransaction;
 
-// Stores hashes of and verifies preference values via
-// PrefHashStoreTransactions.
+// Holds the configuration and implementation used to calculate and verify
+// preference MACs.
+// TODO(gab): Rename this class as it is no longer a store.
 class PrefHashStore {
  public:
   virtual ~PrefHashStore() {}
 
   // Returns a PrefHashStoreTransaction which can be used to perform a series
-  // of checks/transformations on the hash store.
-  virtual scoped_ptr<PrefHashStoreTransaction> BeginTransaction() = 0;
-
-  // Commits this store to disk if it has changed since the last call to this
-  // method.
-  virtual void CommitPendingWrite() = 0;
+  // of operations on the hash store. |storage| MAY be used as the backing store
+  // depending on the implementation. Therefore the HashStoreContents used for
+  // related transactions should correspond to the same underlying data store.
+  virtual scoped_ptr<PrefHashStoreTransaction> BeginTransaction(
+      scoped_ptr<HashStoreContents> storage) = 0;
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_HASH_STORE_H_